This paper examines Just-in-Time (JIT) manufacturing principles in the context of Quality Parts Company, a producer of three gizmo product lines. It identifies proposed managerial changes that conflict with JIT philosophy — including high-rise parts storage, rework lines, and quality control inspector additions — and explains why each undermines lean production goals. The paper then develops quantitative recommendations for scheduling, layout, kanban, and inventory management, sketches a pull-system design, and outlines a concrete plan for introducing JIT. Key suggestions include outsourcing millwork and subassembly functions, renegotiating supplier delivery schedules, and restructuring production runs to more closely match actual customer demand.
Several of the changes being considered by the manager of Quality Parts Company run counter to Just-in-Time (JIT) manufacturing philosophy. The most conspicuous is her request that the industrial engineering department look into high-rise shelving to store parts coming off machine 4. Under JIT principles, parts coming off any machine should be immediately sent to the next machine for further processing — storing them in high-rise shelving creates inventory buffer that JIT specifically seeks to eliminate.
The manager should also hold off on establishing a rework line, even though a 10% scrap rate is inordinately high. Adding a rework line introduces an additional level of complexity to the process that is counter to JIT philosophy. More specifically, if the rework line is only being used to remanufacture 10% of the factory's output, consider how much additional floor space — a scarce resource that must be maximized — will be required just to address that 10% problem, with no guarantee that all scrapped units can be successfully remanufactured. If quality control efforts are effective, a rework line will not be necessary at all.
The third counter-JIT proposal concerns quality control inspectors. If the manager is serious about solving the quality problem, she needs to think about redesigning the assembly process itself to minimize the number of times workers have to handle parts. Human touchpoints are almost always where defects originate. Adding inspectors treats the symptom rather than the root cause.
The fourth issue is that some portion of production time — the exact amount is not specified — must be devoted to manufacturing subassemblies, which are then stored before use. This stockpiling of subassemblies is itself a violation of JIT principles, which call for continuous flow and demand-driven production rather than batch accumulation.
The machines requiring setup time are the mill, lathe, two drills, and the paint booth. Because these setups can be performed concurrently, and because the mill and lathe require the longest setup times, the maximum setup time for the entire assembly line on days when production begins with Gizmo Z (Gz) is 60 minutes, and 30 minutes on days when production begins with either Gizmo X (Gx) or Gizmo Y (Gy).
Actual manufacturing times for the first unit of Gx and Gy are therefore 395 minutes (6.58 hours), and 445 minutes (7.42 hours) for the first unit of Gz. Thereafter, since no single manufacturing step exceeds 50 minutes, the assembly line can produce one gizmo every 50 minutes. This calculation assumes that the paint booth and oven can each operate on only one unit at a time. Assuming further that the factory operates continuously — 24 hours per day, 7 days per week — it can produce the minimum and maximum quantities ordered by the customer in approximately 123.08 hours (5.13 days) and 165.58 hours (6.19 days), respectively. These figures represent theoretical minimums.
Management has currently chosen to produce gizmos in runs of 100 or 300 units. Based on the assumptions above, it takes approximately 11.2 days in total to produce 100 units each of Gx, Gy, and Gz, and approximately 33.5 days to produce 300 units each. In both cases, even assuming the customer consistently orders his maximum volume from Quality Parts, the company is producing units far faster than the customer needs them. The surplus translates directly into additional inventory costs associated with stockpiling completed gizmos beyond the customer's immediate requirements. An important caveat is that some time must be spent manufacturing subassemblies, but the exact duration is unknown.
Altering the manufacturing schedule to more closely match actual customer demand is therefore one clear path to improving the company's profit margin. Lean production principles consistently demonstrate that matching production rates to customer pull reduces both carrying costs and the risk of obsolescence. Another step toward the JIT ideal is to negotiate with vendors so that supplies arrive just as they are needed — rather than arriving randomly as in the current scenario — and to redesign the assembly line so that subassemblies are produced continuously and arrive at other workstations exactly when required.
"Pull system design based on defect and failure analysis"
"Step-by-step roadmap for implementing JIT operations"
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